PCR tests will still detect signature bits of RNA even when the virus is physically broken and no danger at all. Virions are not alive like bacteria are, but they are still more than the pure RNA ("data"). To be infective they need the whole, intact package of RNA and a set of tooling molecules that the parent cell created created alongside the RNA copy (or that were taken from regular cell stocks).

In year 2000 computer terms, the virus doesn't just need the bytes of the VBS file, it also needs the email header that says "ILOVEYOU".